Movement on fibreglass roof's

Hi Beechy, I am a specialist roofer with 20 years experience, not just a so called roofer. sounds to me like there was no room left for the osb3 ply sheets to expand and contract around the perimeter, or simply over tightening the screws holding down the osb3 cans cause the cracking sound. The timber wants to expand with thermal movement but can’t this results in the cracking sound. I’d call the roofers back that did your job and explain how they have incorrectly installed the osb3 under the grp roof. This problem won’t resolve itself I’m sad to say. Grp should only be laid on osb3 t&g boards for most effective results. Normal ply will just delaminate and in attach it’s self, which also could be what the cracking sound is your getting. Hope this helps you out👍🏻

I tend to agree with what the last chap says as their should always be a 20mm gap around the wall abutment edges on the upper deck. This cracking and noise is more related to warm roofs. It can also be a simple thing such as not enough fixings along the joists. On a warm roof deck each joist should be secured along its length at 150mm centres. The noise also can be caused where the wall fillet is pinching against the wall abutments - possibly the lack of a good PU sealant or the wrong sealant used (which does not provide flexibility). If your GRP goes up and over a parapet wall then a movement joint is required. Finally as above - never use straight edge boards on any modern flat roof - always OSB T&G. If this is a warm roof you will be able to see all the fixings in it - sadly you can only see this on cold frosty winter mornings when the roof is covered in frost and there is heat in the room below - this is simply thermal conductivity though the unisulated fixings. Hope this helps Drew @ Fibretechs